Device for analysing the surface of a substrate

ABSTRACT

An analysis device for analysing a transparent or specular surface of a substrate, the device including a raster located opposite the surface of the substrate to be measured, a video camera for capturing at least one image of the raster deformed by the measured substrate, a raster lighting system, and an image-processing and digital analysis mechanism connected to the video camera. The video camera is a matrix array camera, the raster is provided on a substrate having an oblong shape and is bidirectional including a first pattern extending along a first direction and along a smallest extension of the substrate, the first pattern being transversely periodical to the smallest extension, and a second pattern extending in a second direction perpendicular to the first pattern and along a largest extension of the substrate.

The invention relates to a device for analysing the specular ortransparent surface of a substrate, making it possible in particular todetect optical defects either on the surface of this substrate or withinthe volume thereof.

In general, it is sought in industry to achieve ever greater control ofthe quality of manufactured products. In particular, there is at presenta need for permanently evaluating the level of optical quality ofglazing panels.

In particular, it may be desirable to select the flat glass leavingproduction lines in order to use it for a particular application, suchas for example a mirror intended for scientific applications, alaminated glazing panel intended for the building industry, anautomotive glazing panel, such as a windscreen intended in particular tobe highly inclined, or a flat thin glass intended for a display screen.

In general, modern motor vehicle windscreens are particularly monitoredas regards their optical quality. This criterion specifically addressesthe problem of motor vehicle driving safety. Therefore the shape ofwindscreens, their angle of inclination and the manufacturingmaterials—which are very thin glasses or even transparentpolymers—require very careful inspection of the optical quality, whichoften has to be 100% inspection.

Laminated automotive glazing panels require two glass sheets of smallthickness compared with a toughened or tempered monolithic glazingpanel. The production of such thin glass sheets is tricky and may leadto optical defects on the surface or within the volume. These defectsmay become very problematic after assembly for forming a laminatedglazing panel since they cause optical distortion effects that areaccentuated owing to a second glass sheet being joined thereto. Thepresence of such optical defects often results in the glazing panelsbeing scrapped because they are unacceptable. Because the glazing panelshave already been laminated, it is difficult to recycle them and theirproduction cost becomes too high.

It is therefore also desirable to detect such defects as rapidly aspossible on the manufacturing line and in particular before assembling alaminated glazing panel.

The optical defects are often two-dimensional defects, these may besubstrate flatness defects for example or defects within the volume ofthe substrate due for example to the composition of the glass, thesedefects causing light passing through the substrate to deviate.

Also found are defects along a single direction, such as float wavesthat correspond to the signature of the forming process on the floatline, these defects being greater or larger/smaller in size depending onthe quality of the forming process.

The techniques normally used for detecting and evaluating defectsconsist in observing the laminated glazing panel in transmission or inreflection using standardized techniques, such as by visual observationafter assembly of the laminated glazing panel and away from themanufacturing line. As explained above, such inspection is slow and inparticular increases the production cost.

Moreover, specular and transparent surface inspection techniques arecommercially available which make it possible to detect surface defectsby measurements in reflection or in transmission of the glazing panelreflecting the distorted pattern of a reference pattern.

U.S. Pat. No. 6,509,967 describes a method for detecting optical defectsbased on analysing the distortions of a two-dimensional referencepattern observed in transmission. In the case of defects, the image ofthe reference pattern is distorted, and the distortion of numerouspoints of the image is measured so as to deduce therefrom, bycalibration, the optical power along two directions, the values of whichare representative of the presence or absence and the magnitude of saiddefects. This document insists on the need for studied coupling of thereference pattern relative to the camera responsible for the imageacquisition in transmission. Each line of the reference pattern mustcorrespond to an integral number of lines of pixels of the camera.

However, the method of this United States patent requires thecharacteristics of the reference pattern (its dimensions, its shapes andits position) to be known or adapted so as to ensure that the pattern ofthe reference pattern is suitably aligned with the pixels of the camera.Such an alignment is restricting and rarely possible in an industrialenvironment (poor regularity of the reference pattern, expansion of thereference pattern with the variations in temperature over the day, floorvibrations, etc.).

U.S. Pat. No. 6,208,412 provides another measurement method in which aone-dimensional reference pattern is observed in transmission. Themeasurement device of the above document uses a projector to generate areference pattern which forms, on a large screen, always substantiallygreater than the size of the glazing panel to be measured (typically 2×3m), a one-dimensional periodic pattern which is fixed or can vary intime, and also a camera that displays the reference pattern through theglazing panel to be analysed.

The device described in the latter document, although it may besatisfactory in the laboratory or on edge of a production line forquality control by taking samples, cannot however be used for on-lineinspection which has to be exhaustive and carried out without theglazing panels being able to be momentarily stopped.

The incorporation of a projector and a large screen on an industrialline is also rarely possible or desirable, for lack of space. Moreover,the image produced by a projector is in general not very bright. It istherefore essential to shield the screen from spurious ambient light byextensively covering it and even painting the floor black.

Furthermore, to measure defects in two directions in space, since thereference pattern is one-dimensional, the measurement device requiresacquisition of a first image with the reference pattern oriented in agiven direction and then a second image with the reference patternoriented in a perpendicular direction, necessitating the glazing panelstopping during the acquisition, something which is not conceivable onan industrial line, such as for motor vehicles, the glazing panelconveying system of which precludes a temporary stop.

Finally, the measurement method described is a well-known phase-shiftingmethod which consists, with the glazing panel stopped, in successivelyprojecting several, typically four, reference patterns that are offsetin space and in acquiring an image for each reference pattern position,these operations being repeated a second time for the other measurementdirection. This series of acquisitions is therefore very time-consumingand further extends the time during which the glazing panel is stopped.

Consequently, the device described in this patent U.S. Pat. No.6,208,412 and its measurement procedure entail measurement processingtimes that are too long considering the very short times that areimposed on industrial lines for taking the decision to retain or toreject a glazing panel.

The Applicant was thus given the mission of designing a device foranalysing the optical quality of a specular or transparent substratethat does not have the drawbacks of the abovementioned techniques andmakes it possible to detect and quantify defects of this substrate intransmission or in reflection, in an easy, precise and repetitive mannerwhile still meeting all the constraints of implementation on anindustrial line for exhaustive inspection of the glazing panels and inparticular by reducing the cost of glazing panel conformity inspectionon a production line. This innovative device must furthermore make itpossible to use measurement methods that result in the analysis timebeing optimized.

According to the invention, the device for analysing a transparent orspecular surface of a substrate comprises a reference pattern facing thesurface of the substrate to be measured and placed on a support with twodimensions of short and long extents, a camera for capturing at leastone image of the reference pattern distorted by the measured substrate,a reference pattern illumination system and image processing/digitalanalysis means which are connected to the camera and is characterized inthat the support has an oblong shape and the reference pattern isbidirectional, consisting of a first pattern that lies along a firstdirection and along the shorter extent of the support, this firstpattern being periodic transverse to the short extent, and of a secondpattern that lies along a second direction, perpendicular to the firstpattern and along the longer extent of the support, and in that thecamera is a matrix camera.

It will be recalled that a matrix camera is composed of a sensor whichforms a matrix of pixels.

The oblong shape of the support of the reference pattern accompanied bythe use of a matrix camera makes it possible highly advantageously toreduce the area occupied by the reference pattern and thus limit thespace necessary for the device on a production line. Furthermore, theuse of a reference pattern having two patterns extending in twodifferent directions permits direct measurement of the defects that maybe oriented in the substrate along two directions in space.

The magnitude of the patterns of the reference pattern and the positionof the reference pattern, the glass and the camera are of course to beadapted to each type of measurement, which may just as well be theinspection of glazing panels measuring 2 m by 2 m (or more) or solarmirrors as the inspection of glass samples not exceeding 5 cm by 5 cm insize.

According to one feature, the first pattern and the second pattern aredistinct, in the immediate vicinity of and not intersecting each other.

According to another feature, the first pattern is composed of analternating succession of light and dark lines.

According to another feature, the second pattern is formed from asuccession of light and dark oblong lines, the longer dimension of whichlies along the long extent of the support.

According to another feature, the second pattern is formed from a singleoblong line, the longer dimension of which lies along the long extent ofthe support, this line having a contrasted colour relative to thebackground of the reference pattern.

The second pattern, which may be of the order of one millimetre in thecase of a single line or a few millimetres in the case of a successionof a few lines, implies consequently a minimization of the referencepattern.

The width of the elements (for example lines) forming each pattern is infact adapted according to the measurement conditions and the magnitudeof the defects. Preferably, the first pattern and/or the second patterncomprise/comprises at least one line which has, along its short extent,a width of the order of 1 mm to 1 cm. For measurements in reflection onsolar mirrors, the lines of the pattern are for example of the order of1 cm in width, whereas for measurements in transmission on glazingpanels, the lines are of the order of one millimetre in width.

Furthermore, if the support for the reference pattern consists of apanel back-lit by the illumination system, the support panel for thereference pattern may then not exceed 15 cm in width, thereforeconsiderably reducing the dimensions for installing the device of theinvention compared with the existing ones.

As back-lit panel, the panel is, on its face turned towards thesubstrate to be measured, translucent and diffusing. For example, it isa white plastic sheet.

Advantageously, and in particular in the case of back-lighting, theillumination system is formed from numerous light-emitting diodes.

To take a measurement in transmission, the substrate is positionedbetween the reference pattern and the camera, whereas the substrate isplaced facing the reference pattern and the camera for a measurement inreflection, the camera being in the same plane as the reference pattern.

The small dimensions of the reference pattern compared with thesubstrate that is to be measured in its entirety mean that the referencepattern or the substrate can be moved during the measurement.

Thus, compared with the prior art for measurements on large productssuch as glazing panels, the reference pattern does not need to be asextensive in both directions as, or even larger than, the glazingpanels. According to the invention, it is sufficient to provide anoblong reference pattern, the long extent of which corresponds at mostto the height of the object to be measured and the short extent of whichis extremely small compared with the other dimension of the object,combined with a matrix camera.

To meet the need for defects to be analysed simultaneously in two(vertical and horizontal) directions, the device uses a back-litdouble-pattern reference pattern, one consisting of a single verticalline or of very few vertical lines, the other consisting of a series ofvery short (typically 5 cm) uniformly spaced horizontal lines, and amatrix camera, only the columns of pixels of which that are associatedwith each of the two reference patterns will be sampled afteracquisition of the image.

This technique applies both to measurements in transmission and tomeasurements in reflection.

The invention also relates to a method of analysing a transparent orspecular surface of a substrate using the device of the invention, thesubstrate or the reference pattern moving one relative to the otheralong a single displacement direction, characterized in that it consistsin:

-   -   capturing, using the matrix camera, numerous images of the        illuminated reference pattern in transmission or in reflection;    -   spatially extracting in a periodic manner, on the one hand, a        column of pixels associated with the periodic first pattern and,        on the other hand, several columns of pixels associated with the        second pattern;    -   stacking, in memory, the columns of pixels for each of the        patterns so as to reconstruct the image of the entire substrate;    -   analysing the reconstructed image by digital processing so as to        deduce therefrom the position of defects and to quantify them.

The principle of the proposed method consists no longer in acquiring,through a substrate at rest, a single image of a multi-line referencepattern projected onto a large screen but in acquiring a series ofseveral images of a very narrow reference pattern seen through or inreflection from a substrate in translation and in grouping these partialimages so as to reconstruct the complete image of the reference patternseen through or reflected by the substrate.

The digital processing of the image is then carried out in a knownmanner. This involves for example extracting local phases of the imageand deducing therefrom phase variations that make it possible not onlyto deduce the position of defects but also to quantify them thanks tocalibration or distortion coefficients with which a magnitude of thedistortion or an optical power representative of the defects may beprovided.

It should be noted that the digital phase extraction processing may becarried out in various ways using the Fourier transform method or thecontour search method or else, in a novel manner, the wavelet transformmethod.

It appears that the method according to the invention gives satisfactoryresults on industrial lines, without modifying the latter, for lowercost, and permits much more rapid inspection than in the prior art.

The device of the invention and the method of implementation may beapplied to transparent substrates, such as monolithic or laminated, flator curved, glazing panels of any size for various (architectural,automotive, aeronautical, railway) uses or such as mirrors or displayscreens. In particular, the device and the method may be applied intransmission to motor vehicle windscreens, side windows and heated rearwindows, to flat glazing panels intended for architectural applicationsor to special glazing panels intended for electronic applications(plasma or LCD displays, etc.) and to any other transparent substrate.The device may be used in reflection to qualify the optical quality offlat glass, for example in real time as the glass leaves the float bath,or of curved glass as it leaves for example the tempering furnace, ofsolar mirrors, etc.

The present invention will now be described with the aid of purelyillustrative examples that do not in any way limit the scope of theinvention and on the basis of the appended illustrations in which:

FIG. 1 shows a schematic sectional view of an analysis device accordingto the invention for a measurement in transmission;

FIG. 2 shows a schematic sectional view of an analysis device accordingto the invention for a measurement in reflection;

FIG. 3 illustrates an example of a reference pattern according to theinvention;

FIG. 4 illustrates an image of the reference pattern recorded by thecamera.

The figures have not been drawn to scale in order to make it easier toexamine them.

The device 1 illustrated in FIGS. 1 and 2 permits analysing, intransmission and in reflection respectively, the defects of atransparent substrate 2, such as a glazing panel. The device comprises areference pattern 10, image capture means 3, such as a matrix camera, areference pattern illumination system 4 and suitableprocessing/computation means 5.

The reference pattern 10 is formed on one face of a support panel 11facing the substrate to be measured. It will be described more fullylater.

In transmission (FIG. 1), the transparent substrate 2 is placed betweenthe reference pattern 10 and the camera 3, the objective lens of thecamera being directed towards the substrate.

In reflection (FIG. 2), the substrate 2 having a specular surface isplaced in front of the reference pattern 10 and the camera 3, theobjective lens of the camera being in the same plane as that of thereference pattern and being pointed towards the surface of thesubstrate. If an angle of observation has to be imposed so as to beplaced under the conditions in which the product to be measured will befinally used, for example an inclined glazing panel used as a vehiclewindscreen, the angle of the camera relative to the plane ofdisplacement of the substrate corresponds to the imposed angle of thereference pattern relative to this plane of displacement of the glazingpanel.

The illumination system 4 may be a back-lighting system when the supportpanel 11 is translucent, such as a white plastic sheet. Preferably, theillumination system 4 then consists of numerous light-emitting diodesthat are positioned to the rear of the translucent support panel.

As a variant, when the support panel 11 is opaque, the illuminationsystem 4 is formed from a light placed to the front of the referencepattern, for example a spot (not illustrated) oriented so as toilluminate the front face of the support panel bearing the referencepattern.

The camera 3 is a matrix camera: it generates image frames which, bydigital processing, are concatenated to form an overall image of thesubstrate. Since the reference pattern is small compared with thesubstrate, as will be seen later, the substrate 2 or the referencepattern 10 is able to be displaced in translation one relative to theother so as to ensure the requisite number of image acquisitions overthe entire substrate. The frequency with which the camera is triggeredfor each image acquisition is slaved to the speed of displacement.

The camera is positioned at a suitable distance d so as to display theentire extent of the substrate, which is transverse to the direction ofdisplacement of the substrate or the reference pattern. Thus, if thedisplacement is in a horizontal plane, the camera is placed so as tophotograph the entire vertical extent of the substrate.

The camera 3 could make an angle to the vertical adapted to theconditions under which the substrate will be finally used, for exampleif the substrate is then used as a vehicle windscreen and thereforeinclined to the vertical plane of viewing of the driver/observer.

The reference pattern 10, as illustrated in FIG. 3, is placed on asupport 11 of oblong shape. It is bidirectional and consists of a firstpattern 10 a and a second pattern 10 b placed in the immediate vicinityof each other but with no overlap.

The reference pattern according to the invention is small compared withthe substrate to be measured. For example, for measuring a glazing panelwith dimensions of 1.5 m by 1.5 m, the reference pattern extends over 15cm by 1.8 m for a zero angle of inclination of the glazing panel. Formeasurement at a 45° angle of inclination of the glazing panel (in thedriving position for a windscreen), the height will be 1.3 m.

The first pattern 10 a of the reference pattern lies along a firstdirection and along the shorter extent of the support, being periodictransverse to the short extent, i.e. periodic along the long extent ofthe support. The second pattern 10 b lies along a second direction,perpendicular to the first pattern and along the longer extent of thereference pattern.

The fact that the reference pattern has two separate patterns in theimmediate vicinity of each other, but not overlapping, and perpendicularto each other, makes it possible for the position of defects to beprecisely diagnosed and quantified in minute detail. This separation ofthe patterns makes it possible in particular to have a pattern of verynarrow width, such as a dark vertical line 2 mm in width.

The first pattern 10 a is composed of an alternating succession of lightand dark lines.

The second pattern 10 b is preferably formed from a limited number ofcontrasted lines, which alternate but together remain of small width.Thus, the second pattern is for example formed from around ten darklines alternating with around ten light lines. The dark lines and thelight lines have for example a width of between 1 mm and 2 mm over theentire height of the reference pattern.

As a variant, the second pattern may comprise a single oblong line, forexample 1 mm in width, over the height of the reference pattern, thisline being contrasted relative to the background of the referencepattern.

The processing/computation means 5 are connected to the camera so as tocarry out the mathematical processing and analyses that follow thesuccessive image acquisitions.

FIG. 4 illustrates an image recorded by the camera, the image of thereference pattern being distorted by the presence of defects in twodirections. The implementation of the device, the substrate or thereference pattern moving one relative to the other along a singledisplacement direction, consists in:

-   -   capturing, using the matrix camera 3 having numerous pixels 30,        numerous images of the illuminated reference pattern in        transmission or in reflection;    -   spatially extracting in a periodic manner, on the one hand, a        column 31 of pixels associated with the periodic first pattern        and, on the other hand, several columns 32 of pixels associated        with the second pattern;    -   stacking, in memory, the columns of pixels for each of the        patterns so as to reconstruct the image of the entire substrate;    -   analysing the reconstructed image by digital processing so as to        deduce therefrom the position of defects and to determine their        magnitude.

Acquisition of a series of n images of the line forming for example thevertical second pattern, during horizontal displacement of the substratein front of the reference pattern, makes it possible to reconstruct, bysimple concatenation of images, a single image equivalent to that whichwould be obtained by observing just once the image of a referencepattern consisting of n lines placed behind the substrate. The Applicanthas demonstrated that this type of reference pattern is particularlyadvantageous because of its limited size.

A reference pattern is a spatially periodic signal. The mathematicalanalysis consists in characterizing in a known manner this signal by itslocal phase modulo 2π, at a pixel of the camera, and a one-dimensionalmap of the phases (corresponding to all the pixels) of each of theimages seen in transmission or in reflection, called a phase map, isthus defined.

This extraction of the phase map modulo 2π can be obtained using variousmethods.

One well-known method is the Fourier transform method, widely describedin the literature. It can thus be divided into:

-   -   acquisition of an image of the reference pattern distorted by        the specimen;    -   calculation of the Fourier transform of the image, pixel column        by pixel column (one-dimensional transform);    -   automatic search for the characteristic peak of the fundamental        frequency f₀ of the reference pattern;    -   band-pass filtering using a Gaussian band-pass filter, or other        such filter, of this fundamental frequency f₀. The effect of        this filtering is to remove the continuous background of the        image of the reference pattern and the harmonics of the signal        of the reference pattern;    -   shifting of the f₀ filtered spectrum so as to bring the        characteristic peak of the image reference pattern to the        frequency 0. This shift causes the grid lines of the reference        pattern to disappear, leaving only the distortions of the        reference pattern;    -   calculation of the inverse Fourier transform of the image, pixel        column by pixel column. The image obtained reveals only the        distortions. This image is a complex image comprising a real        part R and an imaginary part I;    -   calculation of the local phase at a pixel, modulo 2π, of the        image. This phase is obtained by calculating, pixel by pixel,        the value of arctan (I/R).

Moreover, the Applicant has demonstrated the advantageous use of anothermethod of calculating the local phases, namely a “wavelet transform”method of calculation. This type of calculation used in a known mannerfor signal processing in other applications proves to be particularlyadvantageous in the application of the invention. This is because,unlike the Fourier transform method, which is not a method for localanalysis of the frequencies contained in the image of the referencepattern, the wavelet transform method makes it possible for the positionand the frequency of the signals to be analysed simultaneously. Thisresults in fewer perturbations at the edges of the images (at the edgesof the substrate) and in better detection of small defects that areoften “squashed” during the filtering phase carried out using theFourier transform method.

The wavelet transform technique consists of several steps:

-   -   acquisition of an image of the reference pattern distorted by        the substrate;    -   calculation of the wavelet coefficients W(a,b) from the image        and for various values of the scale parameter a and of the        translation parameter b, pixel column by pixel column        (one-dimensional transform). These values are judiciously chosen        according to the pitch of the reference pattern and the desired        resolution. What is obtained is a wavelet scalogram;    -   for each b value, search for the scale a₀ that maximizes the        modulus |W(a, b)|;    -   calculation of the argument of W(a_(0,b)) that gives at a pixel        the desired local phase modulo 2π;    -   integration or unfolding of the phase map modulo 2π in order to        obtain the absolute phase map.

Once the step of calculating the phase modulo 2π of the image has beencarried out for each pixel by one or the other method, the map of thephase derivatives, also called a gradient map, is easily deducedtherefrom. This calculation of the phase gradient of the image isobtained by simple difference of the phase pixel to pixel, the 2π phasejumps being easily eliminated.

After the phase map of the complete reconstructed image has been deducedfrom the series of images captured by the camera, it is then possible tolink the derivative of the phase at each point of the image to theoptical power Pi of the defects of the glazing panel causing these localphase variations by precalibrating the system using standard cylindricallenses (in transmission) or standard cylindrical mirrors (in reflection)or else using an optical calculation model that enables the opticalpower Pi to be calculated from the derivative of this phase. Bydetermining the optical power and comparing it with a threshold value,it is possible to quantify the defect.

As a variant, the phase derivative will rather be able to be comparedwith a local calibration width that will provide a distortion widthwhich is also representative of the magnitude of the defect.

By quantifying the defect, it is thus possible to establish the opticalquality of a glazing panel under actual conditions of use directly onthe manufacturing line.

Consequently, the method according to the invention for analysing thesubstrate consists:

-   -   in capturing, using a matrix camera, a series of images in        transmission or in reflection of a narrow double-pattern        reference pattern on said substrate without the need, as in the        prior art, for studied coupling of the reference pattern        relative to the camera or for use of a projector and a large        screen;    -   in extracting from this matrix image a few columns of pixels        (for example one for the horizontal reference pattern and five        for the vertical reference pattern) that are associated with the        double-pattern reference pattern;    -   in stacking, in two separate memories (one dedicated to the        horizontal reference pattern and the other to the vertical        reference pattern) of a processing unit for processing these        columns of pixels so as to reconstruct, after the glazing panel        has moved completely in front of the reference pattern (or vice        versa), a complete image of each of the reference patterns seen        through the glazing panel;    -   in extracting the local phases by digital processing, in        calculating the derivative of these phases and in deducing, by        mathematical calculation, the presence of a defect (preferably        using an optical power calculation and its comparison with a        threshold value).

Finally, the proposed measurement device permits exhaustive inspectionof glazing panels present on an industrial line, without sampling them,without either stopping or slowing down the glazing panels, withoutmodifying their position on the conveying system and without using asystem for projecting two reference patterns. The device uses a smallarea compared with the dimensions of the reference pattern, which aremuch smaller than the existing ones; typically, the support panel forthe reference pattern of the invention is 1.8 metres in height by 15 cmin width. Furthermore, the invention makes it possible to limit thenumber of acquisitions for a bidirectional analysis of the defects.

1-12. (canceled) 13: A device for analysing a transparent or specularsurface of a substrate comprising: a reference pattern facing thesurface of the substrate to be measured and placed on a support ofshorter and longer extents; a camera for capturing at least one image ofthe reference pattern distorted by the measured substrate; a referencepattern illumination system and image processing/digital analysis meanswhich are connected to the camera, wherein the support has an oblongshape and the reference pattern is bidirectional, including a firstpattern that lies along a first direction and along the shorter extentof the support, the first pattern being periodic transverse to theshorter extent, and a second pattern that lies along a second direction,perpendicular to the first pattern and along the longer extent of thesupport, and wherein the camera is a matrix camera. 14: A deviceaccording to claim 13, wherein the first pattern and the second patternare distinct, in an immediate vicinity of and not intersecting eachother. 15: A device according to claim 13, wherein the second pattern isformed from a succession of light and dark oblong lines, a longerdimension of which lies along the longer extent of the support. 16: Adevice according to claim 13, wherein the second pattern is formed froma single oblong line, a longer dimension of which lies along the longerextent of the support, the line having a contrasted color relative to abackground of the reference pattern. 17: A device according to claim 13,wherein the first pattern and/or the second pattern comprise/comprisesat least one line which has, along its shorter extent, a width of orderof 1 mm to 1 cm. 18: A device according to claim 13, wherein the firstpattern includes an alternating succession of light and dark lines. 19:A device according to claim 13, wherein the support for the referencepattern includes a panel back-lit by the illumination system. 20: Adevice according to claim 19, wherein the support is, on its face turnedtowards the substrate to be measured, translucent and diffusing, or is awhite plastic sheet. 21: A device according to claim 13, wherein theillumination system includes plural light-emitting diodes. 22: A deviceaccording to claim 13, wherein the substrate is positioned between thereference pattern and the camera for a measurement in transmission,whereas the substrate is placed facing the reference pattern and thecamera for a measurement in reflection, the camera being in a same planeas the reference pattern. 23: A device according to claim 13, whereinthe reference pattern or the substrate is configured to be moved duringmeasurement. 24: A method of analysing a transparent or specular surfaceof a substrate using a device according to claim 13 and such that thesubstrate or the reference pattern moves one relative to the other alonga single displacement direction, the method comprising: capturing, usingthe matrix camera, plural images of the illuminated reference pattern intransmission or in reflection; spatially extracting in a periodicmanner, by the camera, a column of pixels associated with the periodicfirst pattern and plural columns of pixels associated with the secondpattern; stacking, in a memory, the columns of pixels for each of thepatterns so as to reconstruct the image of the entire substrate; andanalysing the reconstructed image by digital processing so as to deducetherefrom a position of defects and to quantify the defects.